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Heat Transfer Operations Mcqs

Q:

We can apply LMTD only when?
(i) There is no change in Specific heats
(ii) Overall heat transfer coefficient is constant
(iii) No heat loss
(iv) No pressure drop

A) (ii)(iii)(iv) B) (i)(ii)(iii)
C) (ii)(iii) D) (i)(ii)(iv)
 
Answer & Explanation Answer: B) (i)(ii)(iii)

Explanation: The LMTD has limitations on its applicability which usually are no change in specific heats overall heat transfer coefficient is constant and no heat loss, but it is totally independent on the pressure drop that takes place in the equipment.

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836
Q:

At fluidisation, the temperature of the bed is _______

A) Constant but non-uniform B) Same for fluid and particles
C) Non uniform D) Increasing from the bottom
 
Answer & Explanation Answer: B) Same for fluid and particles

Explanation: At fluidisation we observe high grade of mixing as the pellets are then behaving as fluids, hence the temperature of the total bed reaches a constant final value.

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559
Q:

At minimum fluidisation with gas flow, which one of the following is correct?

A) All the particles are in fluidisation with random movement B) The particles at the top of the bed are floating in random movement
C) The particles are stable and not moving D) Half or partial quantity of the solids are in random movement
 
Answer & Explanation Answer: D) Half or partial quantity of the solids are in random movement

Explanation: When fluidisation is reached in gas-solid fluidised bed, the terminal velocity for smaller and lesser density particles is reached earlier which makes them free in the tube. Hence we usually observe fluidisation at the point when half or partial quantity of the solids are in random movement.

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543
Q:

The substance used in fluidised bed is _______

A) Same as Packed Bed B) Powdered Substance
C) Large balls D) Finely divided Solid material
 
Answer & Explanation Answer: D) Finely divided Solid material

Explanation: The pellets used in fluidised bed are finely graded solids, such as a tube bundle immersed in a bed of sand or coal particles.

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399
Q:

Which of the following statements are incorrect about Baffles in a Shell and Tube HE?

A) Baffles provide mechanical support to the tubes and help them to be in position B) Baffles streamline the motion of the fluid in Shell side and hence decreases the turbulence
C) The most common type of baffle is segmental baffles D) Baffles increase the overall heat transfer coefficient on the shell side
 
Answer & Explanation Answer: B) Baffles streamline the motion of the fluid in Shell side and hence decreases the turbulence

Explanation: One of the important tasks of a baffle is to increase the turbulence on the shell side so that forced convective effect successfully plays its role and increase the overall heat transfer coefficient. It also holds the tubes in their position as well to provide them with mechanical support.

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355
Q:

The fluidised bed reactor is a ______ reactor.

A) Single phase B) Two phase
C) Three phase D) Gas phase
 
Answer & Explanation Answer: B) Two phase

Explanation: The fluidised bed reactor is either a Gas-Solid or Liquid-Solid phase reactor, as the particles involved also participate in the reactions.

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340
Q:

Which of the following is not a characteristic of a Direct-Contact Exchanger?

A) Only heat Transfer occurs without any Mass -Transfer B) The Exchanger Construction is relatively not expensive
C) The fouling problem does not generally exist, due to the absence of a separating wall (heat transfer surface) between the two fluids D) Very high heat transfer rates are achievable
 
Answer & Explanation Answer: A) Only heat Transfer occurs without any Mass -Transfer

Explanation: One of the important applications of a direct contact exchanger is mass transfer accompanied by heat transfer, such as in evaporative cooling and rectification.

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334
Q:

Which one of the following is not a batch dryer?

A) Agitated vacuum dryer B) Tray dryer
C) Rotary dryer D) Pan dryer
 
Answer & Explanation Answer: C) Rotary dryer

Explanation: Rotary dryer is continuous feed dryer, the batch dryers can be classified as –

Agitated vacuum dryer
Tray dryer
Pan dryer

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